Electrodeposition of leadantimony-tin alloys



Patented Feb. 8, 1949 ELECTRODEPOSITION F LEAD- ANTIMONY-TIN ALLOYS Ralph A. Schaefer, East Cleveland, and James B.

Mohler, Euclid, Ohio, assignors to The Cleveland Graphite Bronze Company, Cleveland,

Ohio, a corporation of Ohio No Drawing. Application November 6, 1943,

Serial No. 509,278

' the deposit is dense, smooth, adherent, and re markably resistant to corrosion. v

One of the main objects of the invention is the replacement of lead in anti-corrosive coatings; another important object is the use of the ternary alloy for bearing surfaces. While electrodeposited lead alone has been Widely used as protective coating owing to its resistance against dilute sulfuric acid and cold hydrofluoric acid as well as some other corrosive agents, the addition of tin and antimony considerably adds to its usefulness in Widening the range of protection against corrosion on the one hand, and in improving the physical properties of the plate such as grain structure and adherence on the other hand. As a bearing liner electrodeposition oi the alloy is an improvement over lead-indium alloys hitherto in use since the antimony is effective, in a way known per se, to contribute to the hardness of the alloy, to its resistance against compression and to its corrosion resistance.

A Wide variation in the composition of the deposited alloy may be obtained according to the proportion of the metal components or the bath, the acid used, and other factors, influencing electro-deposition such as current density and concentration. Addition agents also play an important part in the determination not only of the required smoothness and density of the deposit, but also in the percentage in which the components will be present in the alloy.

As already mentioned above, the electrodeposition of the alloy occurs from acid baths. Although other aqueous acids may be used, we have found it most advantageous to use fluoboric, perchloric, or sulfamic acid baths. With these acids the electrodeposition takes place rapidly, the baths can be easily controlled and the results we obtain are accurate and reproducible.

In preparing the bath we may start with the desired acid and soluble salts of the three metals; or the bath may be made with soluble electrodes and the aid of the electric current. In some cases-we may use a combination of these methods. Thus we may, for instance, prepare a bath with aqueous fluoboric acid as a bath liquid, by dissolving therein basic lead carbonate, stannous sulfate, and antimony trifluoride. Another way 2 Claims. (Cl. 204-43) to proceed is to use a lead salt, thereby first prerparing a lead bath, which is thereafter built up in tin by using a tin anode, and finally built up in antimony by the application of an antimony anode.

A convenient source for lead is white lead or basic lead carbonate. It also proved to be satisfactory to use commercial prepared lead plating salts or lead plating solution.

Tip is usually added as stannous oxide or as a stannous salt. In the latter case it is necessary, in calculating the relative amounts of lead and tin, to consider the fact, that the bath Willbe built up in tin at the expense of a precipitate of lead sulfate.

When antimony is added as a salt, soluble an-- timony fluoride is a convenient addition to fluoborate baths. For other baths, while not being exactly harmful, it is less useful because it limits the type of container used for the bath to those not attackedby acid fluorides.

It will be understood that these methods ofbuilding up the baths are given by way of example only and that it is not intended to limit the invention to the use of the particular substances mentioned.

As already mentioned above, We may build up the bath in part or even entirely by the use of soluble anodes. The anodes may consist of any, one of the three components alone, or we may use lead-tin alloys and antimony. In case we use lead or lead-tin anodes, some antimony will immersion-plate or plate by chemicaldisplacee ment on the anode. We have found, however, that this is not serious since the rate at which antimony immersion-plates on the anode is only about a fourth of the rate at which the antimony is electrodepositin'g at the cathode. The immersion-plate is adherent enough so that the anode may be used two or three times and then the antimony may be scrubbed off and reclaimed. Lead-tin-antimony anodes may also be used, but in this case a greater amount of antimony appears on the surface of the anode during bath operation.

The bath may also be operated with insoluble anodes, such as carbon or platinum. anodes. In this case some lead oxide may be electrodeposited on the anodes. But as in the case mentioned above, the deposition on the anode is not harmful for the process as a whole and the lead may be reclaimed after some time. b

The following examples 'will serve to illustrate the invention more specifically:

Example 1 Fluoboric acid (42%) 450 Basic lead carbonate 278 Antimony trifluoride 4.4 Stannous sulfate 126 Gelatine 0.5

A current density of 20 amperes per square foot will give a good deposit; if the current density is increased, the percentage of tin in the deposit will increase and the percentage of antimony in the deposit will, decrease. If the gelatine in the bath is increased, the percentage of tin in the plate will increase, but the antimony will be little affected. In this as in all other cases the temperature of the bath is maintained at room temperature (about 70 F.)

Example 2 In order to obtain a ternary alloy containing a higher amount of antimony a bath of the following ingredients may be used:

Grams per liter Fluoboric acid (42%) 189 Basic lead carbonate 135 Stannous sulfate 32.6 Antimony trifiuoride 26.4 Gelatine 0.5

centrates from previous baths to make up a fresh bath:

Grams per liter Lead 100-110 Tin -7 Antimony 3-1.4 Fluoborie acid 15-25 (added in the concentrate) Excess fluoboric acid 20 Resorcinol 4-5 Gelatine 1-l.5

The current density and temperature are as in the above examples. Increase in either addition agent will result in an increase of tin in the deposit. If the tin content in the alloy should suddenly drop, we may restore the desired percentage by adding either /2 gram per liter of gelatine or 1 gram per liter of resorcinol.

Example 4 Perchloric acid (70%) -milliliters per liter 2'70 Basic lead carbonate grams per liter 288 Stannous sulfate do 100 Antimony trifluoride do 3 Gelatine do 0.5 Oil of cloves drop per liter 1 is applied at a cathode current density of 20 amperes per square foot at room temperature; a good plate of the ternary alloy containing antimony 2.9%. tin 1.3% is obtained.

Example 5 Another example of bath is: 2 molar lead sulfamate solution milliliters per liter 900 Stannous sulfate grams per liter 100 Antimony trifiuoride do 3 Gelatine do 0.5

011 of cloves drop per liter-.. 1

loath at a cathode current density of 20 ampere per square foot gives a very good plate of the ternary alloy containing antimony 1.3%,

tin 0.8%.

While the above examples, with the exception of Example 2, illustrate the composition of ternary alloys having low contents in tin and antimony, it is possible to electrodeposit plates from the fluoboric bath containing approximately 10% of tin and 10% of antimony. We have also electro deposited ternary alloy containing tin above 20%. We are able to operate this bath at current densities as high as amperes per square foot with good results.

In most cases it is desirable to operate the bath with one of the usual addition agents such as glue, gelatine, oil of cloves, resorcinol and other hydroxy aromatics. However, we have found that the sulfamic acid bath can be operated with good results even without any'addition agents, but in this case a larger amount of tin must be used in the bath to obtain the same percentage in the plate.

Arsenic may be substituted for antimony, or it may be c-odeposited to form either an'arsenicantimony-tin-lead alloy or an arsenic-tin-lead alloy.

The following bath serves as an example:

' Grams per liter Arsenic trioxide 5 At a current density of 20 amperes per square foot, the plate has the following analysis:

Per cent Arsenic 1.67 Antimony 10.6 Tin 11.8

We consider it apparent from the above specification, that the ternary alloy can be deposited over a wide composition range. The bath can b controlled within narrow limits by quantitative analytical methods familiar to those skilled in the art. The bath will not change rapidly in composition if soluble anodes are used.

Other modes of applying the principle of our invention may be employed instead of the one explained, change being made as regards the amount of the metals in the ternary alloy and the method for making the same herein disclosed, provided the ingredients or steps stated by any of the following claims or the equivalent of such stated ingredients or steps be employed;

We'th'erefore particularly point out and distinctly claim as our invention.

1. A method of electroplating an alloy of approximately 12.2% antimony, 1%-2% tin and the balance lead which consists in electrodepositing the alloy from an aqueous bath conslsting essentially offluoborlc acid (42%) 189 grams per liter of bath, basic lead carbonate 135 grams per liter, antimony trifluoride 26.4 grams per liter, stannous sulfate 32.6 grams per liter, gelatin 0.5 gram per liter, the current density being not less than 20 amperes per square foot.

2. A method of electroplating an alloy of approximately 1%-2% antimony, l%-2% tin and the balance lead, which consists in electrodepositing the alloy from an aqueous bath consisting essentially of fluoboric acid (42%) 450 grams per liter of the bath, basic lead carbonate 278 grams per liter, antimony trifluoride 4.4 grams per liter, stannous sulfate 126 grams per liter, gelatin 0.5 gram per liter, the current density being not less than 20 amperes per square foot.

RALPH A. SCHAEFER. JAMES B. MOHLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Thews, Metallurgy of White Metal Scrap and Residues, page '73,'Van Nostrand (1930).

Transactions of Electrochemical Society, vol. 7

28, pages 325-338 (1915).

Transactions of Electrochemical Society, vol. 40, pages 287-304 (1921). 1 

